My truck started recently started running rough and misfiring. It had no power and would hardly take off from the line. I was getting misfire codes, so I upgraded to 8mm plug wires and replaced the plugs.

It ran much better, but still had issues in the 25 - 35 mph range and occasionally felt like it was in 3rd or 4th gear off the line. I could get 3000+ RPMs, but not much power or movement.

Seems like I have been troubleshooting 2 separate issues.

So I changed the tranny fluid and filter, but still no change. I cleared the codes and still see a couple of misfire codes popping up. I'm not sure if my tranny is slipping or if something electrical in the shifter is faulty.

About this same time, I also started a decent oil leak (could be leaking and shorting a sensor?). Is there some way to test the shifting electronics? Is it possible for a tranny shifting solenoid (I'm not sure how the shifting works) or shifting mechanism to fail on one gear? Any ideas on what to look for next?

2001 Disco II
115,000 miles

 

What codes did you get?
Where is the oil leak at?

 

what are/where your codes. When was the last time you changed your tranny fluids/filter. you may want.need to do another change if it has been awhile to clean out any residual goo. are you running premium i.e. 92-93 gas.

 

is it just p0300 to p0308 or are their others like p1171?

 

I got a P0304, P0307, P0308, P1300, and P1590.

I changed the tranny fluid and filter a couple of weeks ago. Yep, running 93 octane in it.

I'm not sure exactly where the oil leak is coming from yet. I'm thinking either back of the valve covers or oil pan.

 

The 1590 code is a Rough Road/ABS fault only indicating the the 3 Amigos are on or come on go.

The random misfires could be bad coil packs. I would make sure that your plugs are seated correctly as well as the plug wires themselves. at night open the hood while running the engine to see if you have any arcing. I had a misfire for a few months replaced the coil packs and then found I had a sticky lifter. their is an oil additive that I used prior to oil change along with a supplement I added to the oil change and that alleviated the sticky lifter issue. For the life of em I cannot remember the name of the company but will pull out my service book next time I go to the truck and get you that.. the one product is called M.O.A..

 

I was wondering about the coil packs. The plug wires are all seated and the wires are new (assuming all is okay there, but I have heard of issues with new wires). I figured if the packs failed, it would be all or nothing. Can I test the packs?

My biggest concern is the transmission slipping. I just did a test drive and it feels like I'm in the wrong gear every time I stop and try to take off again, even if I manually shift down.

 

I would go ahead and change your fluid and filter again. as well as ad some of the Lucas transmission no slip stuff. I am unaware of a means to test the coil packs.
Are you sure that after the last fluid/filter change you are full.

 

So based on the oil leak with these codes and the fact you changed wires and plugs, Start with a compression test because it is easy to do on all cylinders, if it fails, most likely head gasket.

If the all pass then it is more than likely the plugs and wires or coil packs. You might want to try the harbor frieght inline spark tester to help you if it is electrical.

The last test is the fuel system. But since your truck is not throwing lean codes I don't think it is that.


P0304, P0307, P0308, tells me that the issue is with both coil packs if that is the issue. It also tells me that the misfires are happening on both sides of the engine, which means it may not be the head gasket.

So the question is what can it be:

There are four main causes of engine misfires - a loss of spark, an unbalanced air/fuel ratio, a faulty fuel injector and a loss of compression. The loss of a spark could mean that the spark plug needs to be replaced, which is a relatively simple process. It may also be caused by a faulty spark plug wires. In either case, if the spark plugs or wires are failing in one cylinder, they will need to be replaced. When one spark plug or wire goes bad, there's a good chance the others are not far behind. It is a good idea to replace all of the others when replacing one of these components.

If the mixture of fuel and air is too lean - meaning there is more air than fuel - then it will be unable to ignite, even if the spark plugs are working. There is also a possibility that the mixture is too rich - too much gasoline - even though this tends to be far less common than a lean mixture. A gasoline-heavy ratio of air and fuel can occur if the fuel injector leaks, but this tends to occur in all cylinders, not just one, if it happens. An improper mixture can be caused by leaks in the fuel lines, a weak fuel pump or a faulty fuel injector. It is important to check the fuel injector on the problematic cylinder. It should spray a fine mist of fuel, but if there are drips, it may indicate that it is clogged, dirty or otherwise damaged. Low compression can also contribute to engine misfires. Pressure in the combustion chamber is just as important to a healthy cylinder as the fuel mixture and the spark that ignites it.

If a chamber is losing compression, it means that the gasoline and air are leaving the cylinder before they can be ignited. This can be caused by leaky vacuum hoses, a busted exhaust valve or a blown head gasket. When two adjacent cylinders are misfiring, chances are that the gasket between them is cracked or damaged.

 

The rough road signal can fail in the following ways code 1590:
1. Harness or connector damage
2.SLABS failure — wheel speed sensor

A rough road signal failure may be evident from the following:1. HDC / ABS warning light on